Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $59.67   5.726%   $63.0867   $63.09   $63.10   $63.10  
  Purchase #2 $144.81   5.140%   $152.2532   $152.25   $152.25   $152.30  
  Purchase #3 $44.34   6.480%   $47.2132   $47.21   $47.20   $47.20  
  Purchase #4 $47.75   7.239%   $51.2066   $51.21   $51.20   $51.20  
  Purchase #5 $189.65   5.711%   $200.4809   $200.48   $200.50   $200.50  
  Purchase #6 $61.25   7.484%   $65.834   $65.83   $65.85   $65.80  
  Purchase #7 $226.42   3.769%   $234.9538   $234.95   $234.95   $235.00  
  7 purchase totals = $773.89       $815.0284   $815.02   $815.05   $815.10